A semiconductor module, which is mounted on a power apparatus, a railroad vehicle, an automobile, or the like, requires high operating current density and high voltage resistance. Generally, the semiconductor module includes a heat-dissipating structure in which a semiconductor chip, a metal wire, a ceramic insulating substrate, and a heat-dissipating base substrate are bonded by die bonding members considered in terms of a heat dissipation property. Further, a metal substrate is placed between a ceramic insulating substrate and a heat-dissipating base substrate in order to reduce the warpage of the ceramic insulating substrate, and the substrates are bonded by die bonding members. Solder or silver solder has been used in the past as the die bonding member. Recently, active silver solder or the like, which can be bonded, has been applied in addition to lead-free tin-based solder or metal considered in terms of an influence on environmental burden. Tin-based solder is used for bonding between the semiconductor chip and the metal wire and bonding between the ceramic insulating substrate and the heat-dissipating base substrate. At that time, solder cannot be directly bonded to the semiconductor chip and the ceramic insulating substrate regardless of whether or not solder contains lead. Accordingly, metalizing, such as plating, needs to be performed on the bonding surfaces of the semiconductor chip and the ceramic insulating substrate in advance. Active silver solder is used for bonding between the metal wire and the ceramic insulating substrate and bonding between the ceramic insulating substrate and a metal substrate that reduces the warpage of the ceramic insulating substrate.
It is important for the above-mentioned semiconductor module to efficiently dissipate heat generated from the semiconductor chip during operation. For this reason, the respective components of the semiconductor module are required to have high thermal conductivity and a coefficient of thermal expansion that is close to the coefficient of thermal expansion of the semiconductor chip as much as possible; and copper (Cu) or the like is applied for the metal wire, aluminum nitride (AlN) or the like is applied for the ceramic insulating substrate, and Al—SiC, which is made of aluminum (Al) and silicon carbide (SiC), or the like is applied for the heat-dissipating base substrate. Further, since a higher operating current density has been required in recent years, the semiconductor chip has generated more heat. For this reason, the material of the semiconductor chip is about to be changed to silicon carbide (SiC), which is excellent in an operation at a high temperature, from silicon (Si) that has been used until now. In addition, the semiconductor module requires more excellent heat resistance, a more excellent heat dissipation property, and more excellent heat cycle characteristics. Particularly, the appearance of a die bonding member, which significantly affects the thermal reliability of the semiconductor module, has thermal reliability higher than the thermal reliability of existing lead-free tin-based solder or existing active silver solder, and allows bonding, as the die bonding member is expected.
PTL 1 proposes a die bonding member that contains a lead-free low-melting glass composition containing V2O5 and metal particles. According to this die bonding member, the bondability and thermal conductivity of a semiconductor module or a joined body to which any of metal, ceramics, and a semiconductor is bonded can be improved. Further, V2O5—TeO2—Ag2O-based low-melting glass of which the softening point is significantly low is proposed as one example of the lead-free low-melting glass composition containing V2O5, and it is effective that the V2O5—TeO2—Ag2O-based low-melting glass contains 5 to 65 mass % of V2O5, 15 to 50 mass % of TeO2, and 10 to 60 mass % of Ag2O.